“I longed with all my heart to be anyone, anywhere, nowhere, and for it to end.

“I can sit there and think of suicide very logically, the consequences of it, and seriously plan it and work out the what, why and how.”

Asked how her father, whom she recently described as a “brilliant man”, felt about her illness, she smiled: “I think he would be happier if I was not depressed. He’s my dad, he loves me, he wants me to be well.

“He’s there to support me and help me when I ask for it.”

Miss Welby has spoken previously about how privileged she feels, with her “friends, a nice home, a very supportive family nearby, a good church, a good job, a brilliant doctor and an incredibly wonderful boyfriend”.

However, she acknowledged that depression can affect anyone, regardless of background, social standing or stability.

“The fact that I am miserable every day, despite what I have in my life … it’s ridiculous to be depressed in my position but I am,” she added.

She has challenged the Church by claiming that Christians often fail to support or understand people with depression.

Miss Welby works for Livability, Britain's largest Christian disabled charity.

Born in London and raised in Durham, she read theology at Manchester University before joining the police force and patrolling the streets of Hackney, London, for three years.

She had hidden her depression from her parents until last year, when things came to a head and she said she “could not bear the thought of living” any more.

The turning point, she said, was when she started to think of it as an illness as opposed to a part of her, and consequently developed mechanisms to cope.

Sue Baker of the mental health charity Time to Change praised Miss Welby for speaking about her illness so frankly.

"The more people that talk about it, the more people are more confidant talking about it," she said. "It's a fact of life for many of us."